The invention pertains to a method for stitching printed products with a stitching machine, which comprises at least one stitcher head traveling concomitantly with a printed product being conveyed in a product travel direction and at least one concomitantly traveling bending device, and to a stitching machine.
Methods for stitching printed products such as brochures, magazines and the like have been known for a long time. EP 1 629 992 A, for example, discloses a method in which individual printed sheets are assembled on the saddle chain of a saddle stitcher and conveyed in the form of a saddle to a stitching machine. The wire stitch used for stitching is formed in the stitcher head of the stitching machine, which comprises a driver and a bender in the usual manner. The wire stitch driven through the printed product is then closed by a bending device. Between the stitcher head and the bending device there is an intermediate space, through which the printed products to be stitched are conveyed and in which they are stitched. To change the machine over to a printed product with a different product thickness, the stitcher head is shifted vertically either by hand or by a motor.
Through EP 0 958 942 A, a wire stitching machine has become known, which can be adapted to printed products of different thicknesses even during the course of a processing order. For this purpose, the bending device is supported from underneath in such a way that it can move downward and out of the way as needed when the thickness of the printed products to be stitched changes. A hand wheel is provided, which operates by way of a cam to adjust a bending support element to the thickness of the thinnest printed product to be processed. When thicker printed products are delivered to the wire stitching machine, the bending support element moves downward under the opposing force of a spring. To adapt the machine to especially thick, bulky printed products, the control cams of the stitching machine must be replaced.
A stitching device with adjusting means arranged above the stitcher head is known from EP 1 769 937 A. To adapt the machine to printed products of different thicknesses arriving successively during the course of processing, the stitcher head is designed so that it can be shifted vertically by these adjusting means.
It is becoming increasingly important to stitch bulky printed products consisting of a relatively large number of printed sheets assembled prior to the stitching operation. Not only the number of assembled printed sheets but also their folds and the air enclosed between the individual printed sheets contribute to the bulkiness of such products. The printed products to be stitched can comprise a thickness of more than 20 mm. It is difficult, however, to stitch such bulky printed products properly. Although a longer stroke is necessary to stitch bulky printed products, the time available for this is not usually any longer than that available for stitching less bulky printed products. So that stitching can be carried out in a functionally reliable and proper manner, bulky printed products must be precompressed before they are introduced into the stitching machine. The printed products are highly deformed by this, however; in particular, they are flattened out. This can cause the formation of marks, tears, and folded-over sheets. Defective printed products of this type must be discarded.
Finally, a device for producing printed products is known from EP 1 419 898 A, by means of which printed products of different thicknesses arriving in succession can be stitched without manual interventions on the adjusting means of the machine. In addition to a thickness-measuring device connected to a control unit, the machine has for this purpose a setting means, designed as a rotational angle-controlled electric motor, which is also connected to the control unit, and by means of which a bending device can be set to handle printed products to be stitched of a certain thickness; in addition, the height of the bending device can also be adjusted appropriately when the thickness of the succeeding printed product is greater than that of the product preceding it. The use of a rotational angle-controlled electric motor does in fact make it possible to shift the bending device and thus to adjust its height in a variable manner, but it also leads to a not inconsiderable increase in the cost of the machine. This is the case in particular when a machine already equipped with manual height adjustment is to be retrofitted with setting means for adjusting the height of the bending device.